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Tin and its Properties

 

Tin occurs in large quantity as tin(IV) oxide, SnO2 - usually called cassiterite or tinstore.

Extraction from its Ores

The tin ore is roasted in air to remove impurities, such as arsenic and sulphur as volatile oxides. Iron compounds, which might be present as impurities are removed by electromagnetic separation.

The metal is extracted from its ore by carbon reduction. The concentrated ore is mixed with coke and heated in a furnace.

SnO2 + 2C → Sn + 2CO

The tin obtained is purified. It is separated from copper, iron and any other element present as impurities by either thermal -heating beyond it melting point of 232 K, and running off the molten tin, leaving behind any less fusible impurities - or by electrolytic means.

Much purer tin is obtained by the electrolysis of aqueous solution of tin(II) chloride, SnCl2 - the impure tin is made anode, while the cathode is pure tin.

Properties of Tin

Tin shows both physical and chemical properties, which include:

Physical Properties:

1. Tin is solid, with silvery white appearance with lustre.

2. It’s melting point is 231oC.

3. It is malleable and soft (enough to be cut with a knife).

4. It is a good conductor of heat and electricity.

5. It exists in three different forms. These are grey tin of density 5.76 g/cm3; white tin of density 7.28 g/cm3; and rhombic tin of density 6.6 g/cm3.

These allotropes (the different forms) can be converted from one to another by changes in temperature.

grey white rhombic

Grey  reversible reaction arrow 13.2oC White reversible reaction arrow 161o Rhombic   

6. Tin is not ductile enough to be drawn into wires.

Chemical properties

1. With Oxygen - it does not react with oxygen, except at temperature above 1300oC.

Sn(s) + O2(g) → SnO2(s)  at temperatures greater than 1300oC

Hence, It does not corrode or explode in air.

2. With nitrogen and carbon - no reaction occurs.

3. With non metals, example, chlorine - it reacts when heated with chlorine to form tin(IV) chloride.

Sn(s) + 2Cl2(g) → SnCl4(s)

4. With acids - it reacts with acids to different degrees at different concentrations and temperatures. With dilute HCl - no reaction occurs.

With Concentrated HCl the reaction is rapid, producing tin(II) chloride.

Sn(s) + 2HCl(aq) → SnCl2(s) + H2(g)

With dilute H2SO4 - no reaction occurs. With hot concentrated H2SO4 a reaction occurs to release SO2.

Sn(s) + 2H2SO2 → SnSO4(aq) + SO2(g) + 2H2O(g)

With dilute HNO3 - tin reacts with dilute HNO3, forming Sn(NO3)2 and hydrogen.

With conc. HNO3 - tin reacts with conc. HNO3 , forming SnO2.

5. With alkalis - it forms trioxostannate(IV) salts and hydrogen with conc. solutions of alkalis.

Sn(s) + 2NaOH(aq) + H2O(l) → Na2SnO3(aq) + 2H2(g)

Uses of Tin

There are a number of ways tin can be used. These include:

(1). For coating steel - the coating is done by electrolytic method. Tin prevents corrosion in steel, such may be used to can food and drinks.

(2). For making alloys.

(3). Due to its resistance to atmospheric corrosion and low melting point, it can be used to make sheet glass.

  

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